1/**
2 * Copyright (c) 2018 Inria
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Daniel Carvalho
29 */
30
31/**
32 * @file
33 * Declaration of a Least Recently Used replacement policy.
34 * The victim is chosen using the last touch timestamp.
35 */
36
37#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_LRU_RP_HH__
38#define __MEM_CACHE_REPLACEMENT_POLICIES_LRU_RP_HH__
39
40#include "mem/cache/replacement_policies/base.hh"
41
42struct LRURPParams;
43
44class LRURP : public BaseReplacementPolicy
45{
46  protected:
47    /** LRU-specific implementation of replacement data. */
48    struct LRUReplData : ReplacementData
49    {
50        /** Tick on which the entry was last touched. */
51        Tick lastTouchTick;
52
53        /**
54         * Default constructor. Invalidate data.
55         */
56        LRUReplData() : lastTouchTick(0) {}
57    };
58
59  public:
60    /** Convenience typedef. */
61    typedef LRURPParams Params;
62
63    /**
64     * Construct and initiliaze this replacement policy.
65     */
66    LRURP(const Params *p);
67
68    /**
69     * Destructor.
70     */
71    ~LRURP() {}
72
73    /**
74     * Invalidate replacement data to set it as the next probable victim.
75     * Sets its last touch tick as the starting tick.
76     *
77     * @param replacement_data Replacement data to be invalidated.
78     */
79    void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
80                                                              const override;
81
82    /**
83     * Touch an entry to update its replacement data.
84     * Sets its last touch tick as the current tick.
85     *
86     * @param replacement_data Replacement data to be touched.
87     */
88    void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
89                                                                     override;
90
91    /**
92     * Reset replacement data. Used when an entry is inserted.
93     * Sets its last touch tick as the current tick.
94     *
95     * @param replacement_data Replacement data to be reset.
96     */
97    void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
98                                                                     override;
99
100    /**
101     * Find replacement victim using LRU timestamps.
102     *
103     * @param candidates Replacement candidates, selected by indexing policy.
104     * @return Replacement entry to be replaced.
105     */
106    ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
107                                                                     override;
108
109    /**
110     * Instantiate a replacement data entry.
111     *
112     * @return A shared pointer to the new replacement data.
113     */
114    std::shared_ptr<ReplacementData> instantiateEntry() override;
115};
116
117#endif // __MEM_CACHE_REPLACEMENT_POLICIES_LRU_RP_HH__
118